Active control of Cheerios effect for dielectric fluid

This paper presents a novel method of manipulating objects floating on the free surface of dielectric fluids by combining “Cheerios effect” with di-electrowetting. Cheerios effect is a common phenomenon in which small floating objects are either attracted or repelled by the sidewall via capillary effects. The wettability of the sidewall surface is known to be a key parameter for this phenomenon. By controlling the contact angle of the sidewalls via di-electrowetting and thus distorting the adjacent interfaces, Cheerios effect can be controlled to manipulate floating objects. In this control, the titling angle of the sidewall is found to be critical. Theoretical calculation and experimental results are compared for various titling angles and applied voltages. The theory qualitatively agrees with the experiments. Using this method, a linear transportation of millimeter-sized floating object in a channel is achieved. By sequentially applying a voltage to the arrayed di-electrowetting electrodes on the titled sidewalls and by carefully controlling the time interval between switching shifts, the floating object can be propelled continuously along the channel.